EMF is an ubiquitous environmental exposure which may play a role in the induction of cancer. The actions of EMF in biological systems may be enhanced when exposure occurs in combinations with genotoxic insults. As such, plausible mechanism of action of EMF may be modulation of cellular responses to agents which damage DNA. The hypothesis of the proposed program is that EMF exposure alters the molecular regulatory pathways which are normally activated in cells exposed to DNA-damaging agents. The function of these pathways in normal cells is to induce cell cycle arrest, presumably to allow for repair of damage before DNA replication or mitosis takes place. A corollary hypothesis is that the effect of EMF exposure will be pronounced in cells cultured from patients with the genetic disease ataxia-telangiectasia (A-T). A-T cells have defects in DNA damage- induced cell cycle arrest and are sensitive to cell killing and chromosome damage after exposure to other components of the electromagnetic spectrum (i.e. ionizing and ultraviolet radiation). In the proposed experiments, A-T and normal cells will be exposed to bleomycin, a radiomimetic agent which damages DNA, followed by immediate exposure to EMF. Cell cycle progression and DNA synthesis activity will be measured by fluorescence-activated cell sorting (FACS) analysis. The molecular mechanism of EMF will be investigated by measuring components of signal transduction pathways known to be involved in the cellular response to DNA damage. G1/S arrest will be investigated by measuring p53 and related protein expression; DNA synthesis arrest will be investigated by measuring expression of cyclin A; G2/M arrest will be investigated by measuring cyclin B1. To elucidate whether EMF effects are transduced via cellular membranes, the MAP kinase cascade will be investigated by measuring transcription of c-jun and activation of the signal transducing kinases ERK1 and ERK2. Survival of A-T and normal cells following bleomycin/EMF exposure will also be measured, to determine whether EMF effects on cells impact on measurable biologic outcomes. These experiments are designed to investigate EMF effects on proliferation and survival of cells with prior exposure to a genotoxic agent. In addition, the mechanism of EMF action will be investigated by measuring various components of cellular regulatory pathways which lead to inhibition of cell cycle progression. These experiments will also determine whether cells cultured from A-T patients have unusual sensitivity to EMF effects.